Method for testing hearing acuity



May 28, 1963 J. F. JERGER 3,091,234

METHOD FOR TESTING HEARING ACUITY Filed Jan. 18, 1960 I I I I I I I I(TONE) (NOISE) INVENTOR. JAMES F. JERGER AT TOR NEYS United rates Thisinvention relates to methods for testing human hearing acuity, andparticularly for securing relatively precision results for the use of,for example, doctors and surgeons for diagnostic or prescriptivepurposes, or both.

The primary objects of this invention are to provide a new and improvedmethod for effecting relatively precise and dependable hearing tests ofthe foregoing character by direct, expeditious, or time-saving,operations.

Heretofore, methods have been employed for testing the hearing acuity ofhuman ears, and the results of these tests have been recorded and havebeen used in diagnosing the patients hearing condition and inprescribing both medical and surgical treatments, or corrections, as mayseem desirable, including the prescription of compensatorily designed oradjusted hearing aid apparatus for those patients neither desiring norrequiring other treatment. Members of the medical profession, of course,may, and often do, correlate the noted test results with such otherexploratory techniques and observations as may be at their command,including X-ray techniques and direct Visual inspection of the ear partsand associated organic structure. From a consideration of the testresults in combination with information obtained from the notedtechniques, an experienced medical practitioner is placed in a positionto exercise his best judgment in deciding what corrective procedure orprocedures he should prescribe or recommend.

Nevertheless, the known methods of direct testing of the hearing acuityof patients are open to the drawbacks that they tend to be bothtime-consuming and relatively unreliable. For example, one known methodis to apply an air-conducted tone signal of predetermined frequency, asa test signal, to either selected ear of a patient, and of suchintensity that the patient is able to hear the tone signal (at least tosome extent) under normal or quiet conditions, and then to supply abone-conduction masking noise signal to the ears of the patient and toprogressively increase the masking-signal intensity until the patientindicates by any prearranged signal that the testing tone is no longerheard, in that it has then become completely masked. A masking noise issometimes called white noise in that it is preferably composed of adeliberate jumble of sounds covering substantially the entire frequencyrange normally assignable to the human ear and at a rather uniform soundlevel throughout that range. This method is open to the drawback thatmuch time is consumed in obtaining reliable results, in that manydifferent intensities of test signal have to be used to enable a fulldiagnosis to be made, and each such intensity requires masking by aseparate value of masking noise.

In one known form of the above known methods, the noted bone-conductionmasking noise for either selected ear is applied to the bone structureadjacent to that car by a bone-conduction type of electrically actuatedsound generator, or tranducer, and is commonly accomplished through themastoid bone of the skull by way of its skin and flesh covering at amaximum-sensitivity location determined between the tester and thepatient. A drawback peculiar to this form of the method is that thepoint of maximum effective bone conduction to the hearing structure ofthe patient may vary greatly from patient to patient, therebycorrespondingly lessening the value of comparisons of the results forany patient with a normal atent "ice standard. A related drawback isthat, since the masking noise is applied through the mastoid bonesseparately for each of the two cars of the patient, strict reliance on adirect ear-to-ear comparison of the results obtained is not justified.There is no reasonable assurance that the bone structure around one earreceives substantially the same intensity of masking noise as thatreceived by the bone structure around the other ear. Proponents of thismethod commonly depend on a comparison between (1) a quiet thresholdwherein the air-conducted tone signal is applied by ear phones, (2) anair-conduction noise threshold wherein the noise signal is appliedthrough the same earphones, and (3) a bone-conduction threshold with thenoise signal applied to the mastoid bone as above noted.

According to the invention, the foregoing and other drawbacks of knownmethods of testing the hearing acuity of a patient are overcome 'by twomethod features, comprising (l) applying an air-conducted tone-signal ofa selected frequency to the two ears separately, preferably beginning(for either ear) at an initial low intensity which is increasedgradually until the patient first signals that he can just hear it, andcomprising (2) making a similar threshold-ascertaining step for theair-conducted signal while a fixed-intensity hone-conducted maskingsignal is applied to the skull 'by any desired or suitable technique.Preferably the bone-conducted masking signal is applied to the skull ofthe patient to reach both ears about equally, preferably at a locationalong a plane equi-distant from both ears, particularly at about themiddle of the forehead.

The foregoing simplified method is based on a study showing that thebasic causes of a more or less deafened patients hearing difficultiesmay best be diagnosed when the physician is informed quantitatively ofthe patients ordinary air-conducted acuity and is informedquantitatively of his hearing acuity at the cochlea, wherein theauditory nerve ends. The foregoing simplified method, among otherthings, permits the sensori-neural loss (loss between the auditory canaland the auditory nerve) to be estimated with some accuracy and permitsthe condition of the endings of the auditory nerve in the cochlea to beestimated with a related accuracy.

The foregoing simplified method comprehends the use of charts preparedfrom tests according to the recited steps thereof showing the shiftpatterns (between quiet air-conduction threshold and bone-conductedwhite-noise threshold for air-conducted tones) for a large number ofpersons of normal hearing and a large number of persons with the severalknown abnormalities of hearing.

Further according to the invention, a headset structure is providedwhich may be supported by the head of the patient to support, in theproper location, tone-signal air conduction transducers for therespective ears and a noisesignal bone-conduction transducer for theselected location along the median line of the patients skull, therebyfacilitating the testing operation and contributing to obtaining uniformand reliable test results within a relatively short time interval.

The above mentioned and other objects and features of this invention andthe manner of obtaining them will be best understood by reference to thefollowing description of the invention, taken in conjunction with theaccompanying drawing, which schematically illustrates apparatusaccording to the structural aspect of the invention as well as apparatususeful in carrying out the method aspect of the invention.

In the drawing, 1 and 2 may comprise separate sections of a containerfor respective signal sources, which may be housed in separatecontainers if desired. Each section contains an electrical source orgenerator G, G

3 of available construction and a calibrated regulator R, R throughwhich the sound-intensity equivalent of its output, as applied to theear canal or to the bone-structure ,of the patient by the associatedtransducers or transducer,

is visible to the test operator, as by the reading of a volt- 'metercalibrated for sound or energy intensity or by a known dial-and-pointercalibrated-scale arrangement.

Generator G of section 1 is a tone-signal generator.

Its regulator R preferably further includes means for regulating thefrequency in successive steps (four, for eX- ample) over a wide orselected portion of the ear-response frequency range. Section 1 may thuscomprise a commercially available standard clinical audiometer.

Generator G of section 2 comprises the previously noted white-noise, ormasking, generator. Such a generator may sometimes be termed a thermalnoise generator since such generators commonly use, in amplified form,the thermal noise characteristic of a vacuum tube. Regulator R ofsection 2 is expected to be seldom used to raise and lower the outputwith respect to a given noise level, since ideally a single standardintensity of masking noise should be used for all tests for readycomparison purposes. However, that regulator may he used to reduce thenoted standard masking-noise level to a predetermined related lowerlevel for some sensitive patients,

or to raise it to a predetermined related higher level for someverynearly deaf or insensitive patients without departing from theinvention.

Items 4 to 9 comprise the previously indicated headset structure.It'includes a head band 8, to which transducers 4 and 5 are attached(comprising earphones actuatable from the signal or tone generator G ofsection 1), and an extension 7 which supports bone-conduction transducer9, which is electrically excited by the'n'oise generator of section 2,and which is preferably located at about the middle of the forehead ofthe patient when the structure 4 to 9 is in testing position. Thetransducer 9 may be of any usual or desired inertia or bone-conductiontype, being the contact type 'which usually employs a massive internalmember which tends to remain stationary While the outer casing itselftends to partake of a major portion of the electrically suppliedvibratory energy. The headband 8 and the extension arm 7 7 are joined at6, and may the constructed in any usual or desired manner, but arepreferably of such construction that the acoustical interaction betweentransducers 4, 5, and 9 by way of the interconnecting members 7 and 8 ismaintained at a minimum or negligible level. Items 4 and 5 may besponge-rubber padded telephone receivers of any desired type, preferablyof the type which hasa nearly flat response curve over the frequencyrange important in good hearing, such as from 300 to 3000 cycles persecond. The transducer 9 also preferably has a similar flat-responsecharacteristic within the important par of the hearing range offrequencies.

The electrical circuitry over which the transducers 4, 5, and 9 areenergized as desired includes common conductor C, and includesindividual conductors 10 and 11 for transducers 4 and 5 and individualconductor 12 for transducer 9. Switch 3 controls the connection overconductor 12 to transducer 9, while switch 13 applies energizing currentselectively to earphones 5 and 4 according to 'whether it is in itsillustrated position or is in its alternate position. Conductors C and10 to 12 may conveniently comprise separate conductors in the sameflexible cord extending from structure 1, 2 to the transducers, andswitches 3 and 13 may be mounted as a portion of structure in sections 1and 2, or may be included as cord-attached apparatus, as preferred.

Testing procedure according to the invention may be as follows:

(1) First, with both generators G, G not operating or effectivelydisconnected from the headset apparatus,

placed on the patients head that both ears are covered by thetransducers 4 and 5 while the transducer 9 is positioned on the patientsforehead at about 1 to 1 /2 inches above the eyebrows.

(2) Second, the apparatus in section '1 is turned on or adjusted at R ofsection 1 tosupply a predetermined test frequency within the hearingrange of a sub-audible intensity, and the tone signal therefrom (whichreaches transducers 4 or 5 as chosen at switch 13) is increased slowlyat R of section .1 in successive increments until the tone signalbecomes audible to the patient through the ear under test. Thisintensity i recorded as the unmasked hearing threshold for the specificsignal frequency for that ear, following which a similar test and recordis made for the other ear, or may be deferred until the succeedingmethod steps are taken for the initial car, as preferred.

The thresholds for several predetermined unmasked signal frequencies inthe desired range (as 300, 900, 1800, and 2700 cycles per second, orfrequencies of 250, 500, 1000, 2000, and 4000) may be similarly obtainedand recorded for each ear.

(3) Third, a white-noise signal of the noted fixed intensity (loud-noiselevel) is supplied from generator G of section 2, and through switch 3,to bone-conduction transducer 9, which supplies a corresponding level ofwhite noise to the skull of the patient to reach the bone structure atthe respective ears with substantially equal intensity. A calculatednoise level within the skull structure on the order of 40 decibels abovethe standard threshold has been found to be satisfactory.

This white (masking) noise so decreases the effective acuity of thepatients ears that the threshold values previously obtained for eitherear do not apply while the masking noise is present.

(4) The fourth and final testing step is to gradually increase the soundintensity of the tone signal from section 1, for either ear to be testedand at each desired tone-signal frequency, until the tone signal againbecomes just barely audible, which intensity is recorded for that ofboth the masked and unmasked tests for each of the ears and therecording of the results thereof.

The recorded unmasked thresholds may now be compared with each other asto frequency and ear-to-ear variation, and a similar comparison may bemade within the recorded masked thresholds. Finally, the masked andunmasked thresholds may be compared as desired,

thus providing the basis for a logical analysis of the patientscondition to be made by a skilled practitioner, who may or may not bethe person who makes the herein described tests.

While it is generally preferred that the foregoing four steps taken inthe order listed, good results may be obtained if the second recitedstep is deferred until after the recited fourth step. That is, themasked thresholds for the respective ears and for the desiredfrequencies for each ear may be obtained and recorded before theunmasked thresholds are obtained and recorded, but the patient reactionmay be found to be such that more 'accurate overall results are obtainedwhen the steps are taken in the order recited.

A practical advantage of the described increasingsignal aspect of themethod, which applies to obtaining any recited hearing-thresholdreading, is that the patient can signal the threshold value to thetester when the threshold region is reached by an increase in thetesttone intensity (from apparatus of section 1) rather than when thethreshold region is reached by reducing testtone intensity from a levelwell above audibility. Additionally, it has been found that best resultsare obtained when the patient is instructed to signal visually to thetester, as by moving a hand, a finger, or the like when he first barelyhears the tone signal. It may, of course, be advisable under certaincircumstances for the tester to precede the testing steps by holding theheadset apparatus a foot or two away from the patients ears and applyingthe test-tone signal frequencies through one or the other of thetransducers 4, 5 until the patient hears and recognizes the tonefrequencies to be employed for test. This preliminary step, whenemployed, is of course merely to insure that the patient will recognizea test-tone signal upon barely hearing it during the testing operationas hereinbefore described.

It will be understood that the noted intensity of masking noise, orsignal, is that of a loud noise which tends to mask or cover up any andall noises ordinarily present within the quarters suitable for tests ofthe within character. It will be understood, of course, that thevariation, for a given ear and a given frequency, between the unmaskedthreshold and the masked threshold is expected to be on the order of thesound intensity of the masking noise for a normal ear and to bedifierent for an abnormal ear according to the source and extent of theabnormality.

It has been found that the threshold shift produced by a fixed intensityof masking noise is relatively low at the lower frequencies andnoticeably increases with frequency, at least to a certm'n point in aselected frequency range. Accordingly, those test purposes which requirerather uniform threshold shift over the last noted frequency range asrelated to normal-ear response, may be fulfilled by including acompensating filter (within, or suitably associated with, generator G ofsection 2) which gives a relatively large masking noise intensity at thelower frequency ranges and a compensatorily decreasing level for highfrequency ranges. Such filter means form no part of the instantinvention and are therefore not illustrated herein.

It will be understood, of course, that the method herein disclosed ofapplying the test signal from section -1 to the auditory canals of theears under test is preferred primarily because of the obviousselectivity of this method with respect to the two ears of the patient.If that selectivity is not desired, the tone signal may be applied tothe surrounding air generally (as by the conventional so-calledloudspeaker). The disclosed method, of course, has the advantage that atester who may spend a considerable time testing patients selectivity isspared from hearing test-tone signals to any considerable extent.Similar considerations apply to the selection of the bone-conductiontransducer to supply the desired volume of masking noise to the patientsskull. A noise of similar intensity applied through the air to the earsof the patient would be so loud as to be very obnoxious to the testerhimself where several patients are being tested in succession, as wellas tending to penetrate the walls of the enclosure to be a source ofcom.- plaint from persons in surrounding offices, for example.

While I have described above the principles of my invention inconnection with specific method, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention.

I claim:

1. The method of testing a person for sensori-neural hearing loss by thedegree to which air-conducted tones are masked by white noise deliveredby bone conduction directly to the cochlea of the ear under test whichcomprises:

delivering air-conducted pure tones to the ear under test and increasingthe intensity of each said tone to threshold level;

delivering white noise of fixed intensity to the skull bybone-conduction at a point midway between the ears of said person;

then increasing the intensity of each said pure tone to threshold levelin the presence of said white noise; and indicating the intensities ofeach said pure tone. 2. The method of testing a person forsensori-neural hearing loss by the degree to which air-conducted tonesare masked by white noise delivered by bone conduction directly to thecochlea of the ear under test, which comprises:

delivering air-conducted pure tones to the ear under test at thethreshrold intensity level of each said tone and imposing white noise offixed intensity to the skull via a bone conduction pathway through apoint midway between the ears of said person to shift the thresholdintensity level of each identical air-conducted pure tone.

3. The method of testing the character and extent of the impairment of adeafened persons hearing which comprises:

delivering the quiet threshold intensity of at least one air-conductedpure tone to the ear under test by vary ing the intensity of said toneuntil the said tone is just heard by the person and shifting the saidpure tone threshold intensity by applying bone-conducted white noise ata medial point between the ears of said person.

4. The method of testing the hearing of a patient, which comprisesapplying a test tone signal by air conduction to at least one ear of thepatient during a relatively quiet interval and also during a relativelynoisy interval, varying the intensity of the test tone signal duringeach said interval until response of the patient indicates that thethreshold intensity of the .test tone signal is reached, and producingthe said noisy interval for the patient by applying masking noise to thecochlea of his said one ear by way of a bone-conduction path through apoint midway between the ears of the patient.

5. The method of claim 4, wherein the said step of varying thetest-signal intensity during either said interval comprises increasingthe intensity from a sub-threshold value until its threshold value isindicated by response of the patient.

6. The method of testing hearing acuity of a patient, which comprisesapplying a bone-conduction masking noise signal to the skull of thepatient at a location such that it reaches both ears about equally, atthe same time applying an air-conducted test signal to an ear of thepatient, and varying the intensity of at least one said signal untilresponse of the patient indicates that the threshold value of the airconducted test tone signal is reached in the presence of thebone-conducted masking noise signal. 1

7. A method according to claim 6, wherein the said noise signal ismaintained at a fixed relatively high masking intensity while the testsignal is varied in increments of intensity until the patient indicatesthreshold value.

8. A method according to claim 6, wherein the said threshold value isdetermined for each of a plurality of air-conducted test-signalfrequencies dispersed over the nominal hearing range, air-conductedthreshold determinations are made separately with and without the saidmasking noise signal, and air-conducted threshold determina-tions aremade separately for the respective ears of the patient.

References Cited in the file of this patent UNITED STATES PATENTS2,072,705 Bloomheart Mar. 2, 1937 2,217,394 Wengel Oct. 8, 19402,232,779 Fletcher Feb. 25, 1941 2,663,377 Grandjot Dec. 22, 19532,753,397 Zwislocki July 3, 1956 FOREIGN PATENTS 140,904 Australia Apr.23, 1951

1. THE METHOD OF TESTING A PERSON FOR SENSORI-NEURAL HEARING LOSS BY THEDEGREE TO WHICH AIR-CONDUCTED TONES ARE MASKED BY WHITE NOISE DELIVEREDBY BONE CONDUCTION DIRECTLY TO THE COCHLEA OF THE EAR UNDER TEST WHICHCOMPRISES: DELIVERING AIR-CONDUCTED PURE TONES TO THE EAR UNDER TEST ANDINCREASING THE INTENSITY OF EACH SAID TONE TO THRESHOLD LEVEL;DELIVERING WHITE NOISE OF FIXED INTENSITY TO THE SKULL BYBONE-CONDUCTION AT A POINT MIDWAY BETWEEN THE EARS OF SAID PERSON; THENINCREASING THE INTENSITY OF EACH SAID PURE TONE TO THRESHOLD LEVEL INTHE PRESENCE OF SAID WHITE NOISE; AND INDICATING THE INTENSITIES OF EACHSAID PURE TONE.